Embodiments of the invention relate generally to photovoltaic (PV) systems and more particularly to improved systems and methods for forming direct current (DC) electrical connections between a DC connector of a PV panel to a DC connector of a DC-to-alternating current (AC) micro-inverter and AC electrical connections between the micro-inverter and AC wiring harness of the PV system.
PV systems include PV modules arranged in arrays that generate direct current (DC) power, with the level of DC current being dependent on solar irradiation and the level of DC voltage dependent on temperature. PV systems may be constructed either as an inverter system or a micro-inverter system. A typical inverter system uses DC wiring to electrically couple multiple PV panels to a single inverter. The inverter then converts the DC energy from the PV panels into AC energy, such as AC energy suitable for transfer to a power grid. A typical micro-inverter system, on the other hand, uses DC wiring and a junction box to electrically connect a micro-inverter to each PV panel, forming an AC PV module 300 as shown in FIG. 1. In this AC PV module system, each micro-inverter 306 converts the DC energy from its respective PV panel into AC energy suitable for transfer to a power grid. The junction box 308 of each PV module 300 contains bypass diodes that allow each AC PV module 300 to maintain peak efficiency under partial shading conditions by bypassing sections of cells in the AC PV module 300 which are not receiving solar irradiation. By removing AC PV module cells that are not producing DC power from the electrical connection, the PV system ensures that these non-producing AC PV module cells do not draw DC power from the PV system, which may reduce power to the load and cause AC PV module overheating.
The construction of typical AC PV modules makes infield repairs time consuming. In the case of an internal wiring issue, a technician must diagnose the fault onsite in order to determine what component of the module to repair. An electrical fault may occur within the micro-inverter assembly itself 302, which is secured to a PV panel 304, the diodes within junction box 308, or between the two (2) DC connections 310, 312 that contain respective DC connectors 314, 316 that connect the junction box 308 and the micro-inverter 306. Since a unique key or tool must be used to the remove each of the junction box 308, the micro-inverter 306, and to disassemble the DC connectors 314, 316, each component to determine which component of the AC PV module 300 is faulty, the onsite repair is time consuming and costly. Further, the wired connection between the PV panel 304 and the micro-inverter typically includes approximately one to two feet of DC cable and a junction box, which adds cost to the PV system.
To meet the national electrical code (NEC), special DC wiring and grounding specifications exist for DC module strings capable of producing voltages as high as 600 volts. Further, installers must properly manage the safety risks posed by the potentially lethal DC voltages when dealing with installation of DC wiring. As a result, a certified electrician is used for proper installation of the special DC wiring. Because all of the wiring is done on-site, the process for installing the DC wiring of the PV system accounts for a significant amount of the time and cost of the overall installation of the PV system.
AC PV modules are electrically connected together in groups to form multiple circuits within a PV system 322, as shown in FIG. 2. The PV system 322 of FIG. 2 includes a first row 324 of AC PV modules 326 and a second row 328 of AC PV modules 326. An AC wire harness 334 is used to electrically couple AC PV modules 326 to a single AC power output. An AC wire harness 334 is used to electrically connect the AC PV modules within a given circuit to a single AC power output and includes a termination point 330 on one end and a connection point 338 on a second end to connect AC wire harness 334 to the another AC wire harness or the load panel. In installations where the AC PV modules of a given circuit are arranged in multiple rows 324, 328, the AC wire harness is typically arranged to travel down a length of one of the rows of AC PV modules along a first side of a mounting rail, loop around the end of the mounting rail between the adjacent rows of AC PV modules, and then travel down the length of the next row of PV modules along a second side of the mounting rail. Therefore, AC wire harness 334 may be twice as long as rail 332 in order to fully track both sides of rail 332 and connect all AC PV modules 326. Separate AC connections 336 are positioned along the length of the AC wire harness 334 to connect to each PV module 326. Over the length of the AC wire harness 334, power is lost due to cable resistance, which results in lower efficiencies for PV systems with long wire harnesses. This also results in a voltage drop along the length of the AC wire harness. If the AC wire harness 334 is too long, the resulting voltage drop will put the electrical circuit outside of its operating specifications and cause the micro-inverters to turn off, in order to comply with UL safety code. Further, resistance at each connection point along the length of the AC wire harness also results in power loss, and a decrease in efficiency for the PV system.
Therefore, it would be desirable to provide a PV system with DC connections that are easily field repairable, have a reliable and stable connection, and are less costly than the DC connections of known PV systems. It would likewise be desirable to provide an AC wire harness that improves the efficiency of the PV system while decreasing overall costs of the system. It would further be desirable for such a PV system to be manufactured in a manner that reduces the time, cost, and dangers of on-site installation of the PV system.